In recent years, development of a technology for presenting a three-dimensional video has progressed, and a head-mounted display unit (Head Mounted Display; hereinafter referred to as “HMD”) which can present a three-dimensional video having depth has become widespread. Among such HMDs, also an optical transmission type HMD which uses a holographic element, a half mirror or the like to present a three-dimensional video to a user while the user can observe a state of an outside of the HMD in a see-through fashion has been developed. In recent years, improvement in performance of television monitors has progressed, and a three-dimensional monitor which can present a three-dimensional video having depth has become widespread. Although various systems for implementing such a three-dimensional monitor as just described have been proposed, all systems implement three-dimensional video representation having depth by presenting parallax images to a user. Such three-dimensional monitors can present also a two-dimensional video similarly to popular television monitors.